U.S. patent application number 11/995783 was filed with the patent office on 2008-08-28 for optical network monitor pcb.
This patent application is currently assigned to TYCO ELCTRONICS UK LTD. Invention is credited to Juan Tomas Arias, Gerry Branders, Christof Debaes, Hugo Thienpont, Bart Volckaerts, Jan Watte.
Application Number | 20080205885 11/995783 |
Document ID | / |
Family ID | 34897370 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080205885 |
Kind Code |
A1 |
Watte; Jan ; et al. |
August 28, 2008 |
Optical Network Monitor Pcb
Abstract
A fiber pigtailed network monitoring module incorporating an
optical printed circuit board on which a signal-transferring
connection is remotely actuated between electronic components
mounted on the board and active and/or passive optical devices
mounted on the board to generate remotely readable monitoring
signals.
Inventors: |
Watte; Jan; (Grimbergen,
BE) ; Branders; Gerry; (Sint-Truiden, BE) ;
Arias; Juan Tomas; (Alcobendas Madrid, ES) ;
Volckaerts; Bart; (Borgerhout, BE) ; Thienpont;
Hugo; (Halle, BE) ; Debaes; Christof; (Lot,
BE) |
Correspondence
Address: |
BAKER & DANIELS LLP
300 NORTH MERIDIAN STREET, SUITE 2700
INDIANAPOLIS
IN
46204
US
|
Assignee: |
TYCO ELCTRONICS UK LTD
Kessel-Lo
BE
|
Family ID: |
34897370 |
Appl. No.: |
11/995783 |
Filed: |
June 28, 2006 |
PCT Filed: |
June 28, 2006 |
PCT NO: |
PCT/GB2006/002385 |
371 Date: |
January 15, 2008 |
Current U.S.
Class: |
398/25 |
Current CPC
Class: |
G01M 11/3118 20130101;
G01M 11/3136 20130101; H04B 10/071 20130101; G01M 11/3154
20130101 |
Class at
Publication: |
398/25 |
International
Class: |
H04B 17/00 20060101
H04B017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 16, 2005 |
EP |
0514680.8 |
Claims
1. A fiber pigtailed network monitoring module incorporating an
optical printed circuit board on which a signal-transferring
connection is remotely actuated between electronic components
mounted on the board and active and/or passive optical devices
mounted on the board to generate remotely readable monitoring
signals.
2. A module according to claim 1, wherein the connection between
the electronics components and the optical components is
established by polished fiber connectors or by refractive and/or
diffractive micro-optical coupling elements.
3. A module according to claim 1, wherein the said printed circuit
board integrates a battery that can power a CMOS circuit on the
board, allowing to provide current to trigger an electro-optical
component on the board in such a way that triggering of the said
electro-optical component is possible remotely by an optical signal
that impinges on a detector on the said board.
4. A module according to claim 3, wherein the battery is
rechargeable.
5. A module according to claim 3, wherein the electro-optical
component is comprised of a VCSEL or a MEMS-based device.
6. A module according to claim 3, wherein the CMOS circuit can
recognize patterns or codes in the said optical signal so as to
trigger selectively one particular said electro optical component
selected from a plurality thereof.
7. A module according to claim 3, wherein the said electro-optical
component emits a signal that is multiplexed in the output fibers
of the module and this signal can be used for monitoring purposes
or for triggering another electroptical device located further
beyond the splitter branch, allowing to avoid intervention of
technicians in the field.
Description
SUMMARY
[0001] A scalable optical printed circuit board is disclosed that
allows for optical monitoring in a Passive Optical Network (PON),
keeping its passive optical character. The concept of the optical
pcb incorporates a planar waveguide optical splitter, a detector, a
CMOS transistor chip, a rechargeable battery, and a Vertical Cavity
Surface Emitting Laser (VCSEL) array. A distinction can be made
between a solution for a split PON where the splitters are already
deployed in a splitter node and a solution for a new `green field`
PON that still needs to be deployed. For the former, a separate
VCSEL transmitter device can be spliced between the splitter output
port and the fiber of the distribution cable. For the latter, an
integrated module can be spliced to the feeder cable from the
Central Office (CO) and the distribution cable protruding to the
Optical Network Units (ONUs). By means of a trigger signal that can
be recognized by each VCSEL separately and that is multiplexed at
the central office to the downstream traffic, a test pulse is
generated at the splitter node by the VCSEL. The back reflections
of this signal can be measured by an Optical Time Delay
Reflectometer (OTDR) at the central office. This OTDR device can be
shared for measurement of different PON's by means of fiber optic
switches. By appropriate software analysing and reworking the OTDR
data, operators can make a map of the loss evolution of their PON
over time.
BACKGROUND
[0002] In a Passive Optical Network (PON), optical fibers are
deployed in a central split or dual split branch arrangement in
order to distribute signals from the OLT (Optical Line
Transmitters?) in the central office towards a plurality of ONU's
at the subscriber's residence. In order to identify failures in the
network that need to be restored when a subscriber lacks service,
optical time domain reflectometry (OTDR) is used. For a distributed
split PON, this method is inappropriate since OTDR measurements
carried out from the central office cannot distinguish between the
superpostition of the back reflected signals from the splitter
branches. Consequently, it is not possible to locate the fault
after the split branch. As a result, field technicians (technicians
that have to go into the field equipped with an OTDR) are necessary
to do measurements after the split branch to identify possible
failures.
[0003] The negative drawbacks of this approach are (1) that it is a
very expensive method that cannot be used to measure the network
pro-actively on a regular basis; and (2) that for field technician
measurements, connectors are needed in the outside plant in order
to allow for connecting the OTDR equipment to the cable
infrastructure. This can lead to connector failures over time in
case cleaning precautions have not been taken into account by the
field technician crews. In addition, the lifetime of the network
elements where the monitoring has to be carried out is fairly
reduced due to a substantial number of re-entrances in the network
element. Known systems are described, for example, in U.S. Pat. No.
6,396,575 of W. R. Holland (Lucent), U.S. Pat. No. 6,771,358 of M.
Shigeghara and H. Kanomori (Sumitomo), and US Reissue Pat. 36471 of
L. G. Cohen (Lucent).
DESCRIPTION OF THE INVENTION
[0004] A scalable solution for PON monitoring is presented. For a
PON that is already deployed, the monitoring solution can be
implemented by splicing a dual port device (see FIG. 1) or a
multiple port device (see FIG. 2) into the port(s) of a splitter
branch and a fiber(s) of the distribution cable (situation A).
[0005] For a green field PON that still needs to be deployed the
solution consists of an optical pcb, where the planar splitter is
mounted on the board. The connection between the optical devices on
the board is done via optical fibers and fiber coupling devices.
These fiber coupling devices can consist of alignment grooves and
refractive micro lenses. The integrated module has an input port
that can be spliced or connectorised to the feeder fiber and a
multiple output port that can be spliced to the fibers of the
distribution cable going to the ONU's. (situation B).
[0006] A schematic lay out of the concept that is needed for
situation A is depicted in FIG. 1.
[0007] Port (1) is the input port of the device that is spliced or
connected to an output port of the planar splitter. That can be a
250 .mu.m coated fiber, a 900 .mu.m coated fiber, a 3 mm cable, or
a connectorised pigtail with different connectors. The same applies
to the output port (2). The add/drop coupler device (3)
demultiplexes a trigger (pump) signal for activating the VCSEL from
the input port. For this optical device a filter WDM (wavelength
demultiplexer?) can be used or a diffractive (binary diffractive or
Fresnel diffractive) lens system like that described in patent case
U.S. Pat. No. 6,243,513 B1 can be used to decouple the pump from
the input fiber. These micro optic components can if necessary be
mounted on the pcb or chip via flip chip bonding techniques. The
light from the pump signal impinges on the detector. Depending on
the wavelength of the pump signal used, this can be a Si-based
detector or a GaAs detector. A CMOS transistor-chip (5) collects
the optical signal and boosts the power into a charge collector (7)
that is rechargeable each time a VCSEL needs to be activated by a
triggering signal from the Central Office. When an appropriate
digital sequence is received, (intelligence that via the CMOS
circuit can be built into the system) a dedicated VCSEL starts to
emit a short intense pulse. The VCSEL output is collected by
microlenses or other coupling optics into the add port of the
add/drop coupler devices. As a result, the VSCEL signal is coupled
in the output fiber of the transmitter device. This creates an OTDR
pulse that starts in the selected branch and which will only
propagate to one dedicated ONU. The optical sensor (of an OTDR
system) at the CO will consequently receive an OTDR trace of the
only selected branch.
[0008] It is clear that for this situation the pump signal to
trigger the VCSELs is attenuated by the coupler. This solution can
be adopted when the take rates are low and all the splitter ports
are not already connected to an ONU. This should be considered as a
grow-as-you-go method which is of course more expensive than the
other options.
[0009] When the splitter has however no output ports available (in
a "parking lot"), a filter WDM can demultiplex the pump signal from
the splitter port (see FIG. 2a). The configuration of the device
depicted in FIG. 1 is then also different. It basically has N+1
input ports and N output ports. The N+1 input ports need to be
spliced to the N output branches of the splitter and the extra
input port needs to spliced to the pump demultiplexer branch of the
WDM device that decouples the pump light from the downstream
traffic.
[0010] FIG. 2.a shows the configuration when an extra WDM device is
spliced into the feeder fiber and the splitter output port. The
demultiplexer port of the WDM is spliced to the VCSEL array device.
The output ports of the planar splitter are also spliced to the
VCSEL array component.
[0011] FIG. 2b shows the internal configuration of the device
depicted in FIG. 2a. An optical waveguide board with multiple
couplers that couple light from a transmitter array (preferably a
VCSEL array).
[0012] For a green field situation however, the solution would look
like depicted in FIGS. 3a and b. For this situation there are more
options possible. FIG. 3a shows an integrated splitter on board
solution. FIG. 3b shows an integrated splitter on board solution
where the multiplexing of the VCSELs output is accomplished by the
planar waveguide.
[0013] When integrating the planar splitter on the board one can
opt for a planar waveguide device where the splitting of the signal
and the multiplexing of the output of the VCSEL arrays is performed
in the same waveguide (see FIG. 3b). In that case the splitter has
N+1 input ports and N output ports. For N+1 inputs, one port is
used to distribute the power to the N output channels. This input
is spliced to the feeder cable of the CO. The other N inputs are
multiplexed to the output ports and will carry the OTDR pulses from
the transmitter array. The N output ports need to be spliced to the
distribution cable.
[0014] Description of the Design of the Electronic Board
[0015] The electronic interface consists of four main parts. First
of all we have the dedector (or photovoltaic cell) that can consist
of one or more series of connected photodiodes. The material system
(InP, GaAs or Si) depends on the operating wavelength of the
trigger signal sent from the CO. The function of the photodiode
stack is twofold. First, power will be provided via the pump
wavelength to boot up the circuit or to sufficiently recharge the
battery. Then, in a second phase, the power of the pump will be
modulated to provide an identification tag which will select which
transmitter needs to fire up and generate a pulse for the OTDR
trace. Further elements include an ASIC CMOS chip, a rechargeable
battery and an optical transmitter bank (preferably consisting out
of a VCSEL array).
[0016] The functional blocks of the CMOS chip that control the
electronics are depicted in FIG. 4.b. It contains a DC/DC regulator
which will convert energy from the diode into a suitable voltage to
recharge the battery of the module. This can be done by switching
(pulse width modulation) the energy stored inside an inductor. The
next element of the chip is an optical receiver. This is not a
conventional trans-impedance receiver as it should consume minimal
power and is required to operate next to the voltage regulator. A
possible scheme is to use the state of the voltage regulator itself
to sense to the modulation of the pump signal. Indeed, when little
light is impinging on the photodiodes, the regulator will switch
more slowly than when abundant light is falling on the detectors.
It is clear that in this way the data-transfer rate can only be low
(smaller than the PMW rate) but high transfer rates are not
imperative for the application. Another possibility is the use of
an extra dedicated photodiode that is only sensed for receiving the
data-signals.
[0017] The signal from the optical receiver is then transferred to
a local shift register. The clocking is deduced following an
asynchronous serial UART regime (see FIG. 4). This requires an
additional local oscillator (crystal to be included on the
electronic board). Another possibility for clocking is to
synchronize the local clock by receiving alternating one's and
zero's which are sent at the beginning of each triggering.
[0018] When the shift register is filled up, the content is
compared with a predetermined bit-pattern. This bit pattern is used
to very whether the communication is really intented for the
module. After the receiving of the fixed bit pattern the Finite
State Machine (FSM) changes state and the shift register starts now
to receive a new pattern which will uniquely identify one of the
optical transmitters. The FSM controller then checks if the
indicated transmitter number is one of the transmitters for which
the module is responsible. If so, it will power up the driver and
generate an OTDR pulse on the required channel. The module knows
which channels it should respond to since it was pre-programed
during fabrication. The data can be either provided via a
DIP-switch or via a programmable EEPROM. The .mu.-controller
compares the incoming binary data with a internal memory array
which is stored in the .mu.-controller, so that the .mu.-controller
activates the correct VCSEL in the VCSEL array.
[0019] In FIG. 4.B. below the principle is illustrated. To power
the three building parts the dedector, the .mu.-controller and the
VCSEL array, a lithium ion battery can be used or a rechargeable
battery. The battery that can be used is a single cell lithium ion
that produces just enough power to drive the three building parts
used on the board. The recharging of the battery can be done based
on two principles: the first is based on the fact that the
.mu.controller can function as the Li-ion battery charger. For this
approach the principle of a stand alone charging Integrated Circuit
(IC) is used, and this is build in an internal charging program
that is active within the .mu.-controller and we use a Mosfet
component and a sense line to sense the voltage over the battery.
This is already done with a trickle charge system to correctly
charge the battery. The second option is that we use external IC, a
lithium ion battery charger. This IC uses an external power PMOS
device to form a two chip, low cost, low dropout lineair battery
charger. the charge current can be set by an external resistor.
[0020] These two principles are further illustrated in FIG. 4.c.
The recharge of the lithium ion battery is accomplished when there
is no signal on the UART of the .mu.-controller, or we can receive
a specific code on the UART that triggers the .mu.-controller to
recharge the lithium ion battery.
[0021] FIG. 5.a. shows how monitoring can be done in situation A
where the planar splitter is already active in the splitter node.
FIG. 5.b. shows how monitoring is accomplished in situation B where
the planar splitter is not deployed yet and a planar splitter on
board solution can be integrated in an outside plant network
element. By means of a pump signal that can trigger one particular
VCSEL transmitter in a separate device or in an integrated solution
on board, the VCSEL sends out a pulse. This signal is back
reflected and can be demultiplexed in the Central office and
measured by an OTDR. Due to the fact that one particular VCSEL
sending a signal to one of the N ONU's can be triggered, the
problem that for conventional OTDR measurements from the central
office the OTDR signals after the splitter branch are superimposed
is overcome.
[0022] In FIG. 5(a) it is shown that in the Central office (1)
voice and data traffic is multiplexed with video traffic and
connected with the feeder cable, that runs to the splitter node
where the splitting is done at once (centralised) or can be done
over two branches (not shown). An OTDR set up (2) is placed in the
central office and connected to the demultiplexed test signals from
the VCSELs that are placed into the field. For situation A as
described above the transmitter devices (5) that remotely can be
triggered are spliced into the network. Two options are feasible or
N separate devices can be spliced to the splitter output port and
the fibers of the distribution cable (grow as you go option). Or a
WDM device (2) is spliced just before the splitter demultiplexing
the pump triggering signal. The output ports of the splitter and
the demultiplexer port of the WDM can be spliced to the N+1 input
ports of the optical pcb board device housing electronic components
and the VCSEL array (5). Upon triggering a VCSEL the back
reflections can be measured by the OTDR in the central office. The
back reflected signals can provide loss and fault information of
the traject from the splitter node to the tap terminal (6) and the
last drop to the subscriber's residence (7). In FIG. 5b the
greenfield situation is depicted allowing for a connector loss
solution in the outside plant. The monitoring procedure is just the
same as in FIG. 5.a.
* * * * *